[Linux-cachefs] Problems testing Lustre filesystem with fscache / cachefiles

[David Howells]

John Groves <John at groves.net> wrote:

> The main constraint is that I'm stuck, for now, with EL5 kernels due to
> copious dependencies in the Lustre 1.6.* source base.  This is a big issue,
> but it looks like it should not be a deal breaker.  I'm currently running
> kernel 2.6.18-53.1.14.

Where did you get your fscache kernel patches from?

The ones that come built in to the RHEL-5 kernel are unstable.  The newer ones
are much better, but probably not usable with RHEL-5.

> fscache / cachefiles works when /var/fscache is just a directory on my boot
> drive (ext3).  That's nice, but my boot drive is not faster than my network
> (I can stream about 700MB/s over infiniband, and my lustre object servers
> can keep up with that).  My boot drive is good for about 60MB/s.

Yeah.  Caching NFS that's coming over GigE is a complete waste of time if
you're just looking for performance enhancements in what I've observed if
there's no conflicting traffic on the wire.

>    - With ext3 on the ramdisk, cachefilesd dies on startup.

When you say 'dies' does cachefilesd just die, or is there an oops?  Is
anything dumped to dmesg?

> Cachefiles came in the kernel, and I installed cachefilesd with yum.

If it's the RHEL-5 cachefiles, you're probably doomed, unfortunately.  I know
it's unstable, but finding the source of the instability is a pain.  The newer
patches are much better.  I really must try backporting them.

David